1. Field Of The Invention
This invention relates to a chuck assembly for holding releasably a bit member, more particularly to a chuck assembly which is constructed so as to release a bit member conveniently.
2. Description Of The Related Art
Referring to FIG. 1, a conventional chuck assembly includes a hollow chuck body assembly 10, a jaw unit, a rotary shaft 11 and a clutch assembly. A hollow body part (10A) and a top ring member (10B) mounted threadably on a top end of the hollow body part (10A) cooperatively form the chuck body assembly 10. The chuck body assembly 10 has a top surface formed with two opposed keyways 12 and an engaging slot 13 (see FIG. 2) formed on a periphery thereof. The jaw unit includes three clamping legs (L). Each of the clamping legs (L) has a hook portion (L1) formed at an upper end thereof and is received in a corresponding one of the guiding grooves (G1), which guiding grooves (G1) are formed in a seater (G). The seater (G) is disposed in a lower end portion of the chuck body assembly 10. Each of the clamping legs (L) has a lower portion extending outwardly from a lower end of the chuck body assembly 10. A cylindrical driving rod (R) is disposed in the chuck body assembly 10 and has a lower end formed with three hook receiving spaces (R1). The hook portion (L1) of each of the clamping legs (L) engages the hook receiving spaces (R1) of the driving rod (R). The driving rod (R) has a threaded outer wall. The rotary shaft 11 is disposed rotatably in the chuck body assembly 10 and has an upper end portion that extends outwardly from an upper end of the chuck body assembly 10. The rotary shaft 11 has a threaded inner wall such that the rotary shaft 11 engages the driving rod (R) threadably. Since longitudinal movement of the rotary shaft 11 relative to the chuck body assembly 10 is restricted, the rotation of the rotary shaft 11 is converted to the longitudinal movement of the driving rod (R) relative to the rotary shaft 11 so that the driving rod (R) is moved downward to drive the clamping legs (L) of the jaw unit to clamp the bit member (B) when the rotary shaft 11 is rotated in a clockwise direction and so that the clamping legs (L) of the jaw unit are driven to release the bit member (B) when the rotary shaft 11 is rotated in a counterclockwise direction. The upper end portion of the rotary shaft 11 has a periphery formed with a plurality of angularly spaced ratchet teeth 111. Each two adjacent ratchet teeth 111 cooperatively define an engaging space therebetween. A claw plate 14 is mounted pivotally on the top surface of the chuck body assembly 10 and has a claw portion 141. The claw plate 14 is biased by a spring unit 15 to engage the claw portion 141 within one of the engaging spaces so as to restrict undesired rotation of the rotary shaft 11 in the counterclockwise direction. A sleeve member 20 is sleeved on the chuck body assembly 10 and has an inner wall formed with two opposed keys 21. Each of the opposed keys 21 engages a corresponding one of the keyways 12. A pushing projection 22 projects from the inner wall of the sleeve member 20 and is adjacent to one of the opposed keyways 21. The pushing projection 22 has a distal end on which a contact plate 24 is mounted. The contact plate 24 is in slight contact with the claw plate 14 when the rotary shaft 11 is restricted to rotate in the counterclockwise direction. The sleeve member 20 further has a radial hole 25 formed in the periphery thereof and between the pushing projection 22 and the other one of the opposed keys 21. A rotary knob 30 is sleeved on the sleeve member 20 and has an inner wall formed with a through-hole 31 which allows the extension of the upper end portion of the rotary shaft 11 therethrough. A plurality of angularly spaced ratchet teeth 311 are formed on the inner wall of the rotary knob 30 and mesh with the ratchet teeth 111 of the rotary shaft 11 so that the rotary shaft 11 is rotatable with the rotary knob 30.
Referring now to FIG. 2, in a clamping operation, the rotary knob 30 is rotated in the clockwise direction to cause corresponding rotation of the rotary shaft 11 in a known manner. Thus, the driving rod (R) is moved downward to drive the clamping legs (L) to clamp the bit member (B).
Referring now to FIG. 3, in a releasing operation, the rotary knob 30 is rotated in the counterclockwise direction. Due to the provision of the claw portion 141, the rotary shaft 11 is restricted to rotate with the rotary knob 30. In order to rotate the rotary shaft 11 in the counterclockwise direction, the sleeve member 20 must be rotated in the clockwise direction at first in order to cause the contact plate 24 to abut against a contact portion 142 of the claw plate 14 so as to pivot the claw plate 14 in order to remove the claw portion 141 from one of the engaging spaces. At this time, the radial hole 25 is aligned with the positioning slot 13 and an additional tool, i.e. a retaining rod member (not shown), is inserted into the positioning slot 13 through the radial hole 25 in order to retain the contact plate 24 to abut against the contact portion 142 of the claw plate 14. At this stage, the rotary shaft 11 is rotated with the rotary knob 30 so as to move the driving rod (R) upward in order to drive the clamping legs (L) to release the bit member (B).
It is inconvenient and time-consuming to operate an additional tool, i.e. a retaining rod member, when releasing the bit member (B).